Abstract Responding to RFA-RM-17-028, this R21 seeks to examine a novel interpersonal target; namely, parent-teen conversations about teen health behavior change. The scientific premise is that parents have profound impacts on teen risk and vulnerability. Yet parents receive minimal training in the elements of conversations that optimally inspire their children toward engaging in healthy behaviors. A theoretically grounded and reliable taxonomy of behavior change techniques (BCTs) will be used to scientifically derive the conversational elements, or micro-mechanisms, that reduce parent-teen coercion and conflict and facilitate upward spirals of healthy behavior change. We build on a recently completed NICHD-funded R01, in which a behavioral medical regimen to promote engagement in healthy sleep behaviors improved sleep and reduced risk on selected outcomes among 10-18 year olds. This behavioral medical regimen is delivered via 6 individually administered 50 minute sessions, known as the Transdiagnostic Intervention for Sleep and Circadian Rhythms (TranS-C). During the conduct of this research a significant impediment to youth behavior change was coercion and conflict with one or more parent/s. We will recruit parent-teen dyads in which the teen exhibits sleep problems and code two parent-teen conversations: (1) the last 10 minutes of each treatment session, referred to as the `End of Treatment Conversation' and (2) the discussion of a topic of frequent disagreement involving teen behavior change, referred to as the `Hot Topics Task'. Aim 1 involves an iterative process of developing and refining a method to experimentally manipulate parent use of BCTs (n = 8). The product will be referred to as the Parent Behavior Change Intervention (PBC-I). Aim 2 involves a small open trial of the PBC-I (n = 36) to verify target engagement and test if target engagement produces behavior change. Aim 3 examines potential mediators of the relationship between BCT frequency and engagement in sleep promoting behavior and address potential moderators of parent use of BCTs (age/sex of teen, parent/caregiver sex, one or two parent households). Assays from the SOBC repository feature in the methods (e.g., the `Hot Topics Task' is an adaptation of the Couples Conflict Task) and outcomes (i.e., Parent-Child Coercion Scale). Also, the measures are selected to represent various levels of explanation including self-report, behavioral tasks and actigraphy. In terms of the experimental medicine approach, the target is improved interpersonal process between parent and teen. Increased use of BCTs by parents in parent-teen conversations about youth behavior change is a manipulation check. The assays to verify target engagement include the Parent-Child Coercion Scale. The target will be engaged via the development of an experimental manipulation of the target in the form of a novel intervention (i.e., the PBC-I). This 2-year R21 will provide pilot data to prepare for larger scale research that harnesses a novel interpersonal target?the important role of parents in promoting sustainable health behaviors among their teenage children.